Sewage networks are places where various foul-smelling, toxic and/or explosive gases may circulate. These gases generally originate from the decomposition of organic matter and have a tendency to escape via the access shafts (also known as “manholes”) in the form of gas emanations. They may be more abundant in hot weather. These gas emanations may cause people on the surface discomfort or even health problems.
It is generally not possible to seal the access shafts without creating other potential problems. Ventilation is even often essential in order to prevent excessive quantities of gas from accumulating at certain points in the sewage network.
Most modern sewage networks have separate pipes for the foul sewage and the storm water. The storm drain access shafts are closed at the top only by a grating or even a slot of varying widths running along the curbside. These openings are notably able to accommodate rainwater or water from melting snow in order to remove it from the surface and convey it to somewhere where it can be disposed of. The foul sewage access shafts are generally closed by a cover the openings of which are far smaller, notably in order to minimize the amount of gas emanations to the surface.
In spite of this, storm drain access shafts may emit foul-smelling, toxic and/or explosive gases for various reasons, notably in places where the infrastructures use older so-called “combined” sewer storm drain networks. These networks have pipes through which both rainwater and foul sewage circulate. However, because the storm water access shafts of these combined networks need to be used to collect rainwater, their upper opening needs to remain uncovered in all weathers.
Various devices have been proposed in the past to lessen the odors emanating from the drains. For example, U.S. Pat. No. 5,846,274 describes a biofilter which is fitted into an access shaft in order to reduce or eliminate odors therein. U.S. Pat. No. 4,586,941 and EP Patent No. 952263 B1describe devices of a similar kind Other devices also exist.
Many of the known devices may be complex to install or alternatively may entail significant investment. Others use filters which have a tendency to become blocked after a certain time. Active charcoal filters are particularly sensitive to this. It is also difficult to prevent debris, solid or otherwise, from entering the access shaft. These debris may, for example, be sand, dirt, gravel, etc. Some devices may then become blocked or less effective. They will therefore require more intensive and costly maintenance.
Another potential problem is the presence of stagnating water within the access shafts. This water may encourage the hatching-out of mosquitoes or other undesirable insects. Certain insects may carry diseases, for example the West Nile Virus to name but one. It is thus desirable to restrict access by insects to the stagnant water in the bottom of the access shafts.
It is therefore clear that improvements in the technical field concerned were needed.